And because this thing is stationary, T sub one plus T sub two should be equal to 10 newtons plus five newtons. So I'll leave you there. We've done a nice survey of various forces you might see in a first year physics class. And we've been able to think about them in the context of free body diagrams. Physics of the Earth 2nd Ed. still holds up after almost 50 years. At its publishing the Plate Tectonics paradigm was the new revolution and still is. The text touches on the disciplines of Geophysics: Geomagnetics, Gravity (the Tides and the response of the mantle and core and rotation), Radiometric Dating, Seismology and Earthquakes, Earth's ...